CA2894293A1

CA2894293A1 - Breaking device

Info

Publication number: CA2894293A1
Application number: CA2894293A
Authority: CA
Inventors: Timo Kela; Timo Muuttonen; Antti Koskimaki
Original assignee: Sandvik Mining and Construction Oy
Current assignee: Sandvik Mining and Construction Oy
Priority date: 2014-07-03
Filing date: 2015-06-15
Publication date: 2016-01-03
Anticipated expiration: 2035-06-15
Also published as: ZA201504505B; AU2015203560A1; EP2963230A1; CA2894293C; CN105239923A; US20160001432A1; KR20160004941A; KR101699166B1; CL2015001885A1; EP2963230B1; CN105239923B; AU2015203560B2; US9981370B2

Abstract

A breaking device comprising a frame, an impact device comprising a pressure chamber comprising a rear pressure chamber and a front pressure chamber.
The breaking device further comprises a first low pressure port at the rear pressure chamber and a first low pressure channel and a first low pressure accumulator connected to the first low pressure channel. The breaking device further comprises a second low pressure port at the rear pressure chamber substantially opposite to the first low pressure port and a second low pressure channel and a second low pressure accumulator connected to the second low pressure channel. The first low pressure accumulator and the second low pressure accumulator are arranged at the outer circumference of the frame of the breaking device at different positions in the axial direction of the breaking device.

Description

BREAKING DEVICE
FIELD OF THE INVENTION
The invention relates to a breaking device, such as a rock drilling machine or a breaking hammer.
BACKGROUND OF THE INVENTION
The breaking devices, such as rock drilling machines and breaking hammers, comprise an impact device which is intended to provide impact pulses to a tool for breaking material being operated. The impact device com-prises a percussion piston which is a reciprocating object allowed to move to-wards an impact direction and a return direction.
The breaking device comprises a pressure chamber into which the percussion piston is inserted, the percussion piston contributing to divide the pressure chamber into a rear pressure chamber and a front pressure chamber.
For moving the percussion piston into the impact direction, a high pressure is provided into the rear pressure chamber. For moving the percussion piston back, i.e. towards the return direction, a low pressure is provided into the rear pressure chamber, whereby the percussion piston moves back by an effect of a high pressure remaining constantly in the front pressure chamber.
Due to a continuous variation of the pressure of pressure medium in the rear pressure chamber, cavitation may occur in the rear pressure chamber.
The cavitation may, in turn, cause harmful deterioration of the frame of the breaking device or parts of the impact device by incurring small pieces of metal to come off from the frame of the breaking device or from the parts of the im-pact device. This may eventually lead to a leakage of pressure medium via a hole appeared through the wall of the frame of the breaking device or malfunc-tions of the breaking device because of loose pieces entering between moving parts in the impact device.
BRIEF DESCRIPTION OF THE INVENTION
An object of the invention is to provide a novel and improved break-ing device.
The invention is characterized by the features of the independent claim.
According to an embodiment of the breaking device, the breaking device comprises a frame, an impact device comprising a pressure chamber

2 0.0 and a percussion piston, which is an elongated object contributing to divide the pressure chamber into a rear pressure chamber and a front pressure chamber, at least one first low pressure port in the frame at the rear pressure chamber and at least one first low pressure channel extending from the at least one first low pressure port to an outer circumference of the frame of the breaking de-vice, at least one first low pressure accumulator connected to the at least one first low pressure channel at the outer circumference of the frame of the break-ing device, at least one second low pressure port in the frame at the rear pres-sure chamber substantially opposite to the at least one first low pressure port and at least one second low pressure channel extending from the at least one second low pressure port to the outer circumference of the frame of the break-ing device, and at least one second low pressure accumulator connected to the at least one second low pressure channel at the outer circumference of the frame of the breaking device, and wherein the at least one second low pres-sure channel is arranged to extend at least partly in an axial direction of the breaking device, whereby the at least one first low pressure accumulator and at least one second low pressure accumulator are arranged at the outer cir-cumference of the frame of the breaking device at different positions in the axi-al direction of the breaking device.
According to an embodiment of the breaking device, the at least one second low pressure channel is arranged to extend in the axial direction of the breaking device from the at least one second low pressure port towards the front pressure chamber, whereby the at least one first low pressure accumula-tor and at least one second low pressure accumulator are arranged at the out-er circumference of the frame of the breaking device at substantially opposite positions in the radial direction of the frame of the breaking device.
According to an embodiment of the breaking device, the at least one first low pressure channel is arranged to extend substantially in a radial direc-tion of the frame of the breaking device from the at least one first low pressure port to the outer circumference of the frame of the breaking device and the at least one second low pressure channel is arranged to extend at a position of the front pressure chamber, whereby the at least one first low pressure accu-mulator is positioned at the rear pressure chamber and the at least one second low pressure accumulator is positioned at the front pressure chamber.
According to an embodiment of the breaking device, the breaking device comprises at least one first high pressure port in the frame at the front

3 pressure chamber and at least one first high pressure channel extending from the at least one first high pressure port to the outer circumference of the frame of the breaking device, at least one first high pressure accumulator connected to the at least one first high pressure channel at the outer circumference of the frame of the breaking device, at least one second high pressure port in the frame at the rear pressure chamber and at least one second high pressure channel extending from the at least one second high pressure port to the outer circumference of the frame of the breaking device, and at least one second high pressure accumulator connected to the at least one second high pressure channel at the outer circumference of the frame of the breaking device, and wherein the at least one first high pressure channel and the at least one se-cond high pressure channel are arranged to extend substantially in the radial direction of the frame of the breaking device from the at least one first high pressure port and from the at least second high pressure port to the outer cir-cumference of the frame of the breaking device, whereby the at least one first high pressure accumulator is positioned at the front pressure chamber and the at least one second high pressure accumulator is positioned at the rear pres-sure chamber.
According to an embodiment of the breaking device, the at least one first high pressure port and the at least one second high pressure port are ar-ranged at substantially opposite positions in the radial direction of the frame of the breaking device.
According to an embodiment of the breaking device, in the axial di-rection of the breaking device, the at least one first low pressure accumulator and the at least one second low pressure accumulator, as well as the at least one first high pressure accumulator and the at least one second high pressure accumulator are positioned mutually crosswise at substantially opposite posi-tions in the radial direction of the frame of the breaking device.
According to an embodiment of the breaking device, the impact de-vice comprises at least one control valve contributing to divide the pressure chamber into the rear pressure chamber and the front pressure chamber and comprising a number of openings for controlling the flow of pressure medium in the rear pressure chamber through low pressure ports and high pressure ports.
According to an embodiment of the breaking device, the control valve is positioned between the percussion piston and a stationary cylinder comprising openings, and the control valve is arranged to move in respect of

4 the cylinder for controlling the flow of the pressure medium through the open-ings and thereby through the ports for controlling the pressure affecting in the rear pressure chamber.
According to an embodiment of the breaking device, the breaking device is a rock drilling machine.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying draw-ings, in which Figure 1 is a schematic side view showing a rock drilling machine arranged on a feed beam;
Figure 2 is a schematic side view showing a breaking hammer ar-ranged to a distal end of a boom of an excavator; and Figure 3 is a schematic cross-sectional side view of a rear portion of a rock drilling machine and an impact device of the rock drilling machine.
For the sake of clarity, the figures show some embodiments of the disclosed solution in a simplified manner. In the figures, like reference numer-als identify like elements.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows a feasible rock drilling unit 1 which may be connect-ed by means of a boom 2 to a movable carrier, which is not shown. The drilling unit 1 may comprise a feed beam 3 and a rock drilling machine 4 supported on it. The rock drilling machine 4 may be moved on the feed beam 3 by means of a feed device 5. The rock drilling machine 4 comprises a shank 6 at a front end of the rock drilling machine 4 for connecting a tool 7. The tool 7 may comprise one or more drill rods 8 and a drill bit 9 located at a distal end of the tool 7. The rock drilling machine 4 may further comprise a rotating device 10 for rotating the shank 6 and the tool 7 connected to the shank 6. Inside a frame 11 of the rock drilling machine 4 is an impact device 12 comprising a reciprocating per-cussion piston for generating impact pulses to the tool 7. At a drilling site, one or more drill holes are drilled with the rock drilling unit 1. The drill holes may be drilled in a horizontal direction, as shown in Figure 1, or in a vertical direction, or in any direction between the horizontal direction and the vertical direction.
The disclosed solution is known as top-hammer drilling. The features disclosed in this application may be applied in such drilling machines.

, , In an alternative drilling solution, which is known as down-the-hole or DTH ¨drilling, the impact device is located inside a bore hole. Then the im-pact device and a rotating device are located at opposite ends of the drilling equipment. The features disclosed in this application may also be applied in

5 drilling machines of this type.
Figure 2 discloses an excavator 13 provided with a boom 2. At a distal end of the boom 2 there is a breaking hammer 14, which comprises an impact device 12 arranged inside a frame 11 of the breaking hammer 14. The impact device 12 may be in accordance with the solution disclosed in this ap-plication.
In Figures 1 and 2, thus, two different breaking devices 15, namely the rock drilling machine 4 and the breaking hammer 14, are shown. The solu-tion disclosed in this description may be utilized in both kind of breaking devic-es. In the following, the solution is explained as implemented in a rock drilling machine 4. However, the solution may be implemented correspondingly in breaking hammers 14.
Figure 3 shows a schematic cross-sectional side view of a rear por-tion of a rock drilling machine 4 and an impact device 12 of the rock drilling machine 4. The rock drilling machine 4 comprises the frame 11 and the impact device 12 comprising a pressure chamber 16. The impact device 12 comprises further a percussion piston 17, which is an elongated object contributing to di-vide the pressure chamber 16 into a rear pressure chamber 16a and a front pressure chamber 16b when being arranged in the pressure chamber 16 of the impact device 12. During operation the percussion piston 17 is moved forwards in an impact direction A for striking a tool and is moved backwards in a return direction B, the percussion piston 17 thus moving in an axial direction of the rock drilling machine 4. Thus, the percussion piston 17 is reciprocating during a work cycle of the impact device 12. The impact device 12 is hydraulically op-erated whereby the percussion piston 17 comprises one or more first working pressure surfaces 18 affecting in the impact direction A and one or more se-cond working pressure surfaces 19 affecting in the return direction B. The per-cussion piston 17 is moved back and forth by changing hydraulic pressure act-ing on the working pressure surfaces.
The rock drilling machine 4 of Figure 3 comprises further at least one first high pressure port 21 in the frame 11 of the rock drilling machine 4 at the front pressure chamber 16b and at least one first high pressure channel 22

6 extending from the at least one first high pressure port 21 to the outer circum-ference of the frame 11 of the rock drilling machine 4. At the outer circumfer-ence of the frame 11 of the rock drilling machine 4 there is at least one first high pressure accumulator 23 connected to the at least one first high pressure channel 22.
Further, the rock drilling machine 4 of Figure 3 comprises at least one second high pressure port 24 in the frame 11 of the rock drilling machine at the rear pressure chamber 16a and at least one second high pressure channel 25 extending from the at least one second high pressure port 24 to the outer circumference of the frame 11 of the rock drilling machine 4. At the outer circumference of the frame 11 of the rock drilling machine 4 there is at least one second high pressure accumulator 26 connected to the at least one se-cond high pressure channel 25.
In the embodiment of Figure 3 the front pressure chamber 16b and the rear pressure chamber 16a are connected to each other through a third high pressure port 27 at the rear pressure chamber 16a and a connecting channel 28 arranged between the first high pressure port 21 and the third high pressure port 27, as shown schematically by an arrow indicated with the refer-ence sign 28. In practice, the connecting channel 28 may be arranged in the frame 11 of the rock drilling machine 4. Hydraulic pressures affecting the first working pressure surfaces 18 in the rear pressure chamber 16a and the se-cond working pressure surfaces 19 in the front pressure chamber 16b are con-trolled by means of a control valve 20, which may also contribute to divide the pressure chamber 16 into the rear pressure chamber 16a and the front pres-sure chamber 16b. Hydraulic pressures affecting the second working surfaces 19 in the front pressure chamber 16b and in the rear pressure chamber 16a may thus be affected by the control valve 20 through the connecting channel 28. The control of the working cycle of the percussion piston 17 is generally known to a person skilled in the art and is therefore not described in more de-tail here.
The purpose of the first high pressure accumulator 23 is to maintain high pressure in the front pressure chamber 16b for providing an effective re-turn movement of the percussion piston 17. The purpose of the second high pressure accumulator 26 is to provide an auxiliary high hydraulic pressure in the rear pressure chamber 16a for intensifying the impact movement of the percussion piston 17. The high pressure accumulators will thus increase a

7 working operating efficiency of the impact device 12. The actual adjustments or settings of pre-charge pressures in the first 23 and second 26 high pressure accumulators are selected such that a proper operation of the impact device 12 is achieved.
The at least one first high pressure channel 22 and the at least one second high pressure channel 25 are arranged to extend substantially in the radial direction of the frame 11 of the rock drilling machine 4 from the at least one first high pressure port 21 and from the at least one second high pressure port 24 to the outer circumference of the frame 11 of the rock drilling machine 4, whereby the at least one first high pressure accumulator 23 is positioned at the front pressure chamber 16b and the at least one second high pressure ac-cumulator 26 is positioned at the rear pressure chamber 16a and any pressure losses between the high pressure accumulators 23, 26 and the respective front 16b and rear 16a pressure chambers will remain at their minimum.
With the feature the radial direction of the frame of the rock drilling machine it is meant the direction from the centre of the frame 11 of the rock drilling machine 4 towards the outer circumference of the frame 11 of the rock drilling machine 4 and with the feature substantially in the radial direction of the rock drilling machine it is meant the direction which deviates not more than degrees from the radial direction of the frame of the rock drilling machine.
The rock drilling machine 4 of Figure 3 comprises further at least one first low pressure port 29 in the frame 11 of the rock drilling machine 4 at the rear pressure chamber 16a and at least one first low pressure channel 30 extending from the at least one first low pressure port 29 to the outer circum-ference of the frame 11 of the rock drilling machine 4. At the outer circumfer-ence of the frame 11 of the rock drilling machine 4 there is at least one first low pressure accumulator 31 connected to the at least one first low pressure chan-nel 30.
Further the rock drilling machine 4 of Figure 3 comprises at least one second low pressure port 32 in the frame 11 of the rock drilling machine at the rear pressure chamber 16a substantially opposite to the at least one first low pressure port 29. Further the rock drilling machine 4 comprises at least one second low pressure channel 33 extending from the at least one second low pressure port 32 to the outer circumference of the frame 11 of the rock drilling machine 4, and at least one second low pressure accumulator 34 con-nected to the at least one second low pressure channel 33 at the outer circum-

8 ference of the frame 11 of the rock drilling machine 4. The at least one second low pressure channel 33 is arranged to extend at least partly in the axial direc-tion of the rock drilling machine 4, whereby the at least one first low pressure accumulator 31 and the at least one second low pressure accumulator 34 are arranged at the outer circumference of the frame 11 of the rock drilling ma-chine 4 at different positions in the axial direction of the rock drilling machine 4.
When the rock drilling machine 4 is provided with at least two mutu-ally substantially radially opposite low pressure ports 29, 32, where low pres-sure accumulators 31, 34 are connected to, a cavitation effect, which typically is focused to radially opposite position with respect to a single low pressure port, may be avoided. With the feature substantially radially opposite it is meant that an angle between 170 ¨ 190 degrees, preferably exactly 180 de-grees, remains between the first 29 and the second 32 low pressure ports, whereby the cavitation effect may be successfully avoided. Further, when the at least one second low pressure channel 33 between the at least one second low pressure port 32 and the at least one second low pressure accumulator 34 is arranged to extend at least partly in the axial direction of the rock drilling machine 4, the actual position of the second low pressure accumulator 34 at the outer circumference of the frame 11 of the rock drilling machine 4 may be selected substantially freely with respect to other components, such as high pressure accumulators, mounted at the outer circumference of the frame 11 of the rock drilling machine 4. This is especially useful when updating old con-structions of rock drilling machines comprising originally a single low pressure port in the rear pressure chamber 16a but a need to add an additional low pressure port has arised due to the cavitation effect but the actual locations of other components at the outer circumference of the frame 11 of the rock drill-ing machine 4 does not allow an additional low pressure accumulator to be added exactly at the same position in the axial direction of the rock drilling ma-chine 4 where the additional low pressure port has been located.
In the embodiment of Figure 3 the at least one second low pressure channel 33 is arranged to extend in the axial direction of the rock drilling ma-chine from the at least one second low pressure port 32 towards the front pressure chamber 16b, whereby the at least one first low pressure accumula-tor 31 and at least one second low pressure accumulator 34 are arranged at the outer circumference of the frame 11 of the rock drilling machine 4 at sub-stantially opposite positions in the radial direction of the rock drilling machine 4.

9 In this way the at least one second low pressure port 32, the at least one se-cond low pressure channel 33 and the at least one second low pressure ac-cumulator 34 may be provided in the rock drilling machine 4 in a simple way.
However, the at least one second low pressure channel 33 could also extend in a direction which deviates from the exact axial direction of the rock drilling machine 4 and still the advantageous effects against the cavitation effect would be achieved.
In the embodiment of Figure 3 the at least one first low pressure channel 30 is arranged to extend substantially in the radial direction of the rock drilling machine 4 from the at least one first low pressure port 29 to the outer circumference of the frame 11 of the rock drilling machine 4. Furthermore the at least one second low pressure channel 33 is arranged to extend at the posi-tion of the front pressure chamber 16b. In the embodiment of Figure 3 the se-cond low pressure channel 33 comprises two portions, i.e. a first portion 33a extending substantially in the axial direction of the rock drilling machine 4 away from the second low pressure port 32 to a position at the front pressure cham-ber 16b and a second portion 33b extending substantially in the radial direction of the rock drilling machine 4 from the first portion 33a towards the outer pe-riphery of the rock drilling machine at the position of the front pressure cham-ber 16b. The second low pressure accumulator 34 is connected to the second portion 33b of the second low pressure channel 33 at the outer periphery of the frame 11 of the rock drilling machine 4. The at least one first low pressure accumulator 31 is thus positioned at the rear pressure chamber 16a and the at least one second low pressure accumulator 34 is positioned at the front pres-sure chamber 16b. However, the implementation of the first 30 and second 33 low pressure channels as well as the positioning of the first 31 and second 34 low pressure accumulators could also vary from that disclosed in Figure 3.
Furthermore, in the radial direction of the frame 11 of the rock drill-ing machine 4 of the embodiment of Figure 3, the at least one second high pressure port 24 is arranged substantially opposite to the at least one first high pressure port 21, whereby, in the axial direction of the rock drilling machine 4, the at least one first high pressure accumulator 23 and the at least one second high pressure accumulator 26 as well as the at least one first low pressure ac-cumulator 31 and the at least one second low pressure accumulator 34 are positioned mutually crosswise at substantially opposite positions in the radial direction of the rock drilling machine 4. This means that the low pressure ac-cumulators 31, 34 and the high pressure accumulators 23, 26 are arranged at the outer circumference of the rock drilling machine 4 in such a way that the lengths of respective pressure channels remain as short as possible in the cir-cumferential direction of the frame 11 of the rock drilling machine 4 in order to 5 ensure effective operation of the respective pressure accumulators.
In the embodiment of Figure 3 the control valve 20 is positioned be-tween the percussion piston 17 and a stationary cylinder 35, which comprises a first part 35a positioned substantially at the rear pressure chamber 16a and a second part 35b positioned substantially at the front pressure chamber 16b.

10 The cylinder 35 may also contribute to divide the pressure chamber 16 into the rear pressure chamber 16a and the front pressure chamber 16b.
The control valve 20 comprises openings 36, 37 and the cylinder 35 comprises openings 38, 39, whereby when the control valve 20 moves in re-spect of the cylinder 35 during the operation of the impact device 12, the con-trol valve 20 controls the flow of the pressure medium through the openings 36, 37, 38, and 39 and thereby through the ports 24, 27, 29 and 32 for control-ling the pressure affecting in the rear pressure chamber 16a. The cylinder 35 comprises also an opening 40 which provides a flow connection between the first high pressure port 21 and the front pressure chamber 16b. The embodi-ment of the control arrangement comprising the control valve 20 and the cylin-der 35 as disclosed in Figure 3 is only one possible implementation for the control arrangement to be used in the impact device 12, and the actual imple-mentation of it may thus vary from that disclosed in Figure 3.
It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The in-vention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. A breaking device (15) comprising a frame (11), an impact device (12) comprising a pressure chamber (16) and a percussion piston (17), which is an elongated object contributing to divide the pressure chamber (16) into a rear pressure chamber (16a) and a front pres-sure chamber (16b), at least one first low pressure port (29) in the frame (11) at the rear pressure chamber (16a) and at least one first low pressure channel (30) ex-tending from the at least one first low pressure port (29) to an outer circumfer-ence of the frame (11) of the breaking device (15), at least one first low pressure accumulator (31) connected to the at least one first low pressure channel (30) at the outer circumference of the frame (11) of the breaking device (15), at least one second low pressure port (32) in the frame (11) at the rear pressure chamber (16a) substantially opposite to the at least one first low pressure port (29) and at least one second low pressure channel (33) extend-ing from the at least one second low pressure port (32) to the outer circumfer-ence of the frame (11) of the breaking device (15), and at least one second low pressure accumulator (34) connected to the at least one second low pressure channel (33) at the outer circumference of the frame (11) of the breaking device (15), and wherein the at least one second low pressure channel (33) is arranged to extend at least partly in an axial direction of the breaking device (15), whereby the at least one first low pressure accumulator (31) and at least one second low pressure accumulator (34) are arranged at the outer circum-ference of the frame (11) of the breaking device (15) at different positions in the axial direction of the breaking device (15).

2. A breaking device as claimed in claim 1, characterized in that the at least one second low pressure channel (33) is arranged to extend in the axial direction of the breaking device (15) from the at least one second low pressure port (32) towards the front pressure chamber (16a), whereby the at least one first low pressure accumulator (31) and at least one second low pressure accumulator (34) are arranged at the outer circumference of the frame (11) of the breaking device (15) at substantially opposite positions in the radial direction of the frame (11) of the breaking device (15).

3. A breaking device as claimed in claim 1 or 2, character-ized in that the at least one first low pressure channel (30) is arranged to extend substantially in a radial direction of the frame (11) of the breaking de-vice (15) from the at least one first low pressure port (29) to the outer circum-ference of the frame (11) of the breaking device (15) and the at least one se-cond low pressure channel (33) is arranged to extend at a position of the front pressure chamber (16b), whereby the at least one first low pressure accumula-tor (31) is positioned at the rear pressure chamber (16a) and the at least one second low pressure accumulator (34) is positioned at the front pressure chamber (16b).

4. A breaking device as claimed in any one of preceding claims, characterized in that the breaking device (15) comprises at least one first high pressure port (21) in the frame (11) at the front pressure chamber (16b) and at least one first high pressure channel (22) ex-tending from the at least one first high pressure port (21) to the outer circum-ference of the frame (11) of the breaking device (15), at least one first high pressure accumulator (23) connected to the at least one first high pressure channel (22) at the outer circumference of the frame (11) of the breaking device (15), at least one second high pressure port (24) in the frame (11) at the rear pressure chamber (16a) and at least one second high pressure channel (25) extending from the at least one second high pressure port (24) to the out-er circumference of the frame (11) of the breaking device (15), and at least one second high pressure accumulator (26) connected to the at least one second high pressure channel (25) at the outer circumference of the frame (11) of the breaking device (15), and wherein the at least one first high pressure channel (22) and the at least one second high pressure channel (25) are arranged to extend sub-stantially in the radial direction of the frame (11) of the breaking device (15) from the at least one first high pressure port (21) and from the at least second high pressure port (24) to the outer circumference of the frame (11) of the breaking device (15), whereby the at least one first high pressure accumulator (23) is positioned at the front pressure chamber (16b) and the at least one se-cond high pressure accumulator (26) is positioned at the rear pressure cham-ber (16a).

5. A breaking device as claimed in claim 4, characterized in that the at least one first high pressure port (21) and the at least one second high pressure port (24) are arranged at substantially opposite positions in the radial direction of the frame (11) of the breaking device (15).

6. A breaking device as claimed in claims 2 and 5, character-ized in that in the axial direction of the breaking device (15), the at least one first low pressure accumulator (31) and the at least one second low pressure accumulator (34), as well as the at least one first high pressure accumulator (23) and the at least one second high pressure accumulator (26) are posi-tioned mutually crosswise at substantially opposite positions in the radial direc-tion of the frame of the breaking device (15).

7. A breaking device as claimed in any one of preceding claims, characterized in that the impact device (12) comprises at least one control valve (20) contributing to divide the pressure chamber (16) into the rear pressure chamber (16a) and the front pressure chamber (16b) and comprising a number of openings (36, 37) for controlling the flow of pressure medium in the rear pressure chamber (16a) through the high pressure ports (24, 27) and the low pressure ports (29, 32).

8. A breaking device as claimed in claim 7, characterized in that the control valve (20) is positioned between the percussion piston (17) and a stationary cylinder (35) comprising openings (38, 39), and the control valve is arranged to move in respect of the cylinder (35) for controlling the flow of the pressure medium through the openings (36, 37, 38, 39) and thereby through the ports (24, 27, 29, 32) for controlling the pressures affecting in the rear pressure chamber (16a).

9. A breaking device as claimed in any one of preceding claims, characterized in that the breaking device (15) is a rock drilling machine (4).